Omnifocus creates an iCal export of due tasks. It doesn't create reminders though, and the sync is only one way. You have to handle the todos under OmniFocus, the iCal feed is just to inform you about your tasks.

iCal, called Calendar since Mountain Lion, supports iCalendar format version 2. Org-mode - an organizer and information manager with many additional features - can export to iCalendar format. Org-mode comes by default on Emacs text editor.

Install Emacs from GNU Emacs for Mac OS X, create an org-mode file (.org extension), then press C-c C-e i (or run org-export-icalendar-this-file) to export the current file to an .ics file, which you can then open in Calendar program.